Important Note:
Blair's post at the top of this thread refers to changing the read/write permissions of the actual folder that DirectRT / MediaLab live in. This is typically C:\MediaLab or C:\DirectRT for the 2008 versions.
If you just right-click on the MediaLab / DirectRT icon on your desktop, then it will change the permissions only on the shortcut--not on the main folders and so changes won't have the desired impact.
So the important note again here: Be sure to use the file explorer / My Computer shortcut and apply these changes to the program folder.